Sugden A21/A51 diy pcb: anybody? - Page 2 - diyAudio
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Old 11th December 2011, 12:46 AM   #11
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Default Sugden 21 Mk 3 or later

Dear All,

I have a Sugden A28 Mk 3 which according to the schematic I have is much the same as a A48 Mk 3 but with 71 V rather than 73.6V power supply, and uses 120 VA transformers rather than 140 VA.

Unlike Sugden DIY design but like the Sugden A21 Mk2/A51, in the A28 mk3 the feedback goes to Tr1's Emitter.

The with the exception of the circuit driving the output transistors it is in essence the same topology but with a constant current phase splitter as this amp is a class AB bias heavily into class A.

To my ears at least ( no distortion measurements or equipment suitable for doing this) this is the nicest amplifier I have by some margin. Followed by the Quad 303, the Quad 306 and then many other amps I have had. The old JLH design I made years ago (without enough spent on the transformers) has never been compared as they are in different countries.

I would be very interested in a Sugden A21 Mk3 or later schematic, as I would not be surprised if it is essentially a scaled up A51 with modern components (probably lower distortion) and optimized for 4-6 Ohm speakers. Such a clone (with a PCB) would probably tempt me to build it as the A28 Sugden box is not so much better than that of a DIY design.

Some one with more knowledge than I, would I expect clone the Sugden A51 with a few more constant current sources. My uneducated guess is that (Referring to the A51 schematic) R13/R14 and R18 should be replaced with a constant current supply. I imaging the bias of Tr1 could be made more conventional. I personally don't understand what X2 is for.

How would the experts on the forum improve upon a Sugden A51?

Regards

Owen
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Old 11th December 2011, 11:05 AM   #12
rmgvs is offline rmgvs  Netherlands
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Hallo Owen,

I had several A28/A48 in the past (original ones, not diy), and though good they are not in the class of the old A21 and A51. It remains to be seen why this is so (use of parts, power supply, circuit diagram, distortion spectrum etc), but for me this is the starting point.

The design is kept rather constant during time, mostly newer parts and some circuit revisions. But it's open secret that the old design still is the best in terms of subjective quality like mellowness (new design sounds more hifi).

So the A51 with common available parts and a good power supply on a well laid out pcb can be the answer. Must be on the same level as JLH and Hiraga, and (having all of them on a diy basis) personally I like to listen to the Sugden the most.

Well, this is all words. Now the waiting is on somebody who has the time and wisdom to design a suitable pcb.
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Old 11th December 2011, 02:23 PM   #13
jez is offline jez  United Kingdom
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I have an A21 and although it's good in terms of "warmth" etc I wouldn't personally rate it all that highly overall..... It does indeed sound very similar to 60's valve amps but that includes the soft bass, slightly rounded top end etc.
I am re-opening a catering pack of worms here but to me an amp should be accurate not "Nice". And by accurate I mean just that... NOT harsh, grainy, rounded or anything else.
BTW Be wary of later versions of these amps as when they reached I think MKIII they became a different amp in the same case and no longer class A !
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Old 12th December 2011, 06:44 AM   #14
rmgvs is offline rmgvs  Netherlands
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Jez, you are right of course. It's an old discussion. I think that all good amps that have become classics have less or more euphony in the sound. Hiraga, JLH, some Pass amps, Sugden, the A1/A100/A1000: they all do not sound clinical but err on the side of warmth.

BTW: all these class-A classics do sound slightly different in some respects (and of course one piece can sound different on its own depending on how you build it).

An amp that gives it all would be the preferred option: warmth, details etc. Most of the amps that give a lot of details and are considered neutral or accurate, don't give me much pleasure at the end of the day. And let's be honest, that's what it is all about.
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Old 12th December 2011, 06:29 PM   #15
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Dear Jez,

I think some of it has to do with what speakers your driving. Accurate low bass is not essential in an amplifier if your driving electrostatics and Quad ESL 63's roll off their treble around the same place as my hearing, since they don't go down so low.

The Quad 306 is defiantly a lot better in low bass than my other amps but is some times grating (harsh in the higher frequency regions) but then maybe thats the source material being accurately reproduced. Although some of the other power amps under the bed sound nice in the bass department, for me its all about how they sound in the human voice region. Some how the Sugden A28 Mk3 is more reach out and touch it, closely followed by the Quad 303's. Though it must be said I will test the Net audio power supply module soon (its coming hopefully before Christmas) to see how it compares with original Quad 303's and if it can match my Sugden A28 then.

I am not yet sure what for me makes a great amp, but would be very tempted build a Sugden clone as I can always convert it to a JLH Class A/Hiraga if it fails to beat my current champion.

Regards

Owen
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Old 12th December 2011, 07:24 PM   #16
jez is offline jez  United Kingdom
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Beauty is in the ear of the beholder.... That's one sleeping dog that I should never have kicked!
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Old 12th December 2011, 08:02 PM   #17
AKSA is offline AKSA  Australia
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In most cases, tagboard amps will sound better than pcbs anyway because of lower parasitics. I hear this again and again.

Take care with the thermal design of this amp; the original gets VERY hot indeed because the fins are horizontal, not vertical.

Hugh
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Old 12th December 2011, 08:34 PM   #18
jez is offline jez  United Kingdom
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Quote:
Originally Posted by AKSA View Post
In most cases, tagboard amps will sound better than pcbs anyway because of lower parasitics. I hear this again and again.

Take care with the thermal design of this amp; the original gets VERY hot indeed because the fins are horizontal, not vertical.

Hugh
I think it very unlikely that tag board would result in any substantial difference to the sound. Parasitics can be just as low (lower in fact) with pcb's....
I've nothing against tagboard and I'm familiar with it's reputation but I reckon it's all more snake oil to justify certain highly priced "boutique" amps both in hifi and guitar amps. YMMV.
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Old 12th December 2011, 09:10 PM   #19
AKSA is offline AKSA  Australia
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Yes, Jez, my mileage does vary!!

Greetings from sunny Oz,

Hugh
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Old 12th December 2011, 11:30 PM   #20
jez is offline jez  United Kingdom
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Quote:
Originally Posted by AKSA View Post
Yes, Jez, my mileage does vary!!

Greetings from sunny Oz,

Hugh
Fair dinkum Hugh! My bro (Simon) done one and left the sinking ship... Married one of you colonials and now has a restaurant in your area... It gets very good reviews Chester White | Home Page Ask him how the pre-amp I made him is doing if you go and tell him his brother sent you....
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